Pinch flats are caused when you ride into something that causes a sharp impact — a rock, railroad track or edge of a pothole are prime culprits. The impact compresses the tire so much that the tube is pinched between it and edges of the rim.
This causes 2 small holes about half an inch apart on the rim side of the tube. They look like fang marks, so that’s why pinch flats are also known as snakebite flats.
Most pinch flats are caused by a combination of 3 factors: not enough inflation pressure, tires that are too narrow and/or poor riding technique.
The first line of defense is inflating tires to the “sweet spot” — hard enough to avoid pinch flats but not so hard that ride comfort and handling are compromised. As a tire gets harder, it becomes more unyielding when it hits the small bumps that are part of any road surface.
The result is a tire that’s skittish and prone to chattering in turns. Some authorities speculate that this slows you down because the tire is, in effect, bouncing off each bump in the road and momentarily reducing your forward momentum. I’m not qualified to judge if that’s correct, but I like the feel of some “give” in my tires.
Generally, riders up to 190 pounds on smooth roads can safely and comfortably run 90-100 psi in the rear tire and about 80-90 psi in the front. Experiment to find the pressure that works best for you.
Wider tires help protect against pinch flats because they contain more protective air volume. Consider using 700x25C or even 700x28C tires if pinch flatting is a problem. If your fork doesn’t have enough clearance for wider tires, run the widest size you can on the rear and use a narrower size up front.
Recently, riders have adopted lower pressures and wider tires after research, much of it done by Jan Heine at Bicycle Quarterly, showed that speed didn’t change appreciably with widely different tire pressures while comfort increased with both lower pressures and wider tires. Even pro racers have gone from 23mm tires to 25s and even 30mm on some courses. Research also shows that tires with supple casings are faster than those with rigid sidewalls.
As for technique, pay attention to the road surface. When you spot a potential tire biter that you’re not going to be able to miss, slow down and think “light.” Bend your elbows and knees, level the pedals, raise your butt off the saddle and let the bike “float” over the hazard. Riding with the right tire width and air pressure will save you most of the time when you hit something unexpectedly.